This invention relates to a sizing apparatus for an internal grinder whereby an oscillation machining of an inner peripheral surface of a work piece can be performed and a bore of the work piece can be measured by means of a sizing device during the oscillation machining.
In FIG. 12, a spindle feeding table 10 (work table) is movable in the direction of Y and a wheel spindle table 12 is movable in the direction of X which is perpendicular to the Y direction. A work piece 14 is supported on the spindle feeding table 10 and a grinding wheel 16 is supported on the wheel spindle table 12.
The grinding wheel 16 is fitted on the tip of a drive shaft of a spindle motor 18, and the inner peripheral surface of the work piece 14 is ground by the grinding wheel 16.
As shown in FIG.. 13, the spindle feeding table 10 is driven in the Y direction by a feeding motor 24 by way of a ball type screw 20 and a speed reducer 22 which are disposed under the table 10, thereby actuating the grinding wheel 16 to grind the inner peripheral surface of the work piece 14.
As shown in FIG. 14, the wheel spindle table 12 is stroked and driven in the X direction by means of a traverse motor 26 and a ball type screw 28 which are disposed under the table 12, and is vibrated by means of an eccentric cam 30 and an oscillation motor 32.
The tips of a pair of forks 36 included in a sizing device 34 arranged on the spindle feeding table 10 are inserted into the work piece 14 from a side of the sizing device nearer the grinding wheel 16, and are pressed toward the inner peripheral surface of the work piece 14, as shown in FIG. 15, 16, 17, 18 and 19.
Positions of the tips of the forks 36 are measured by means of a sizing device 34, and the bore of the work piece 14 is obtained by virtue of the measured positions of the tips.
As shown in FIG. 17 and 18, when the bore of the work piece 14 is small relative to the size of the grinding wheel 16 and, the grinding wheel 16 and the tips of the forks 36 interfere with each other during an oscillation machining, the tips of the forks 36 are inserted into or removed from the work piece 14 by means of an interlocking mechanism 38 relative to an oscillation of the wheel spindle table 12 interlocked therewith.
In an example in FIG. 12, the sizing device 34 is movable in the direction of axis of the work piece 14 (X direction), and is driven forward and backward on a shaft 40 of the interlocking mechanism 38 relative to the work piece 14.
The center portion of the shaft 40 is supported by a guide 42, and the base end of the shaft 40 is fixed on an interlocking member 44.
The interlocking member 44 is driven by a drive member 46 provided on a side of the spindle motor 18 by way of a shaft 48, and is urged in the direction where the tips of the forks 36 are inserted into the work piece 14 by means of a spring 50. The shaft 48 is supported by guides 51 and 53.
A contactless switch 49 is disposed in proximity to the interlocking member 44 on the spindle feeding table 10, and is turned on when the tips of the forks 36 touch the inner peripheral surface of the work piece 14 during an oscillation machining, as shown in FIG. 20.
A switching signal for the contactless switch 49 is used as a size locking signal for sizing signal outputted from the sizing device 34. The sizing signal of the sizing device 34 is invalidated when the contactless switch 49 is off, and is treated as effective only when the contactless switch 49 is on.
Therefore, the sizing signal corresponding to the bore of the work piece 14 is intermittently obtained during an oscillation machining.
Thus, the size locking signal which removes unnecessary portions of the sizing signal and effects only necessary portions thereof is turned on at a time t.sub.1 caused by a time of delay .DELTA.t after the tips of the forks have reached the end surface of the work piece at a time shown with (A) t.sub.0 and, is turned off at a time t.sub.3 before a time t.sub.5 when the tips of the forks retreat from the end surface of the work piece 14, in the case that the wheel spindle table 12 moves at a speed whose oscillation cycle is extremely low, as shown in FIG. 20.
To the contrary, in the case that the wheel spindle table 12 moves at a speed whose oscillation cycle is extremely high, a delay time .DELTA.t is substantially increased to an non-negligible degree relative to the oscillation cycle, thereby resulting in a delay in a time t.sub.4 for turning off the size locking signal.
Namely, a hysteresis always exists in the switching of the contactless switch 49, as shown in FIG. 20 (A), and a shut-off time t.sub.4 of the size locking signal moves toward a shut-off time t.sub.5 of the sizing signal by means of the sizing device 34.
Therefore, when a length d of the work piece in the axial direction is extremely short, as shown in FIG. 20, a shut-off time t.sub.4 of the contactless switch 49 is delayed compared to a time t.sub.5 when the tips of the forks 36 retreat from the end surface of the work piece 14, whereby the bore of the work piece 14 cannot be measured.